Based on detail information of riser and last inspection data,main degradation mechanisms were determined.Corrosion rate was assessed according to relevant standards and documents.Based on the defect detected and the corrosion rate,failure probability of riser under new developed defect was calculated by Ameliorated First-Order Second-Moment(AFOSM).Curve of failure probability of riser varying by time was delineated.According to the accepted criterion of riser failure,inspection plan involved.In addition,new inspection results were viewed as the information of next analysis.Safety and economy were both satisfied by this risk inspection method.Moreover,references can be provided to corrosion failure analysis of other pipes used in sub-sea production system.

The installing of SSIS can reduce the fire and explosion consequences caused by offshore platform leakage,but if the SSIS fails when there is an accident on offshore platform,it can cause worse consequences.So it is necessary to evaluate the reliability of SSIS.Based on FTA and basic event failure probability obtained from the database,the failure probability of three classical types of SSIS assemblage is calculated,the strengths and weaknesses of each types were analyzed according to the failure probability,and the failure probability of SSIS can be the basis of the reliability research on SSIS.

Diffusion radius and fountain height are necessary for the risk analysis of underwater gas diffusion.The method,coupled with the VOF model and DPM model in FLUENT,was taken to simulate the underwater gas diffusion,which is leaked from piping in the vertical direction.The behavior of the interface between water phase and air phase was simulated,the bubble particles diffusion process was researched and the diffusion radius and axial displacement were analyzed.The effects on the rising time and fountain height from different flow rates were discussed.Compared to the experiment data of rising time and fountain height,the method is correct in some condition.

It's found in the tests of pipelines' buckling that the original sealing technique of the deep-water pressure container is time-consuming,ineffective,insecure and always unsuccessful.For these phenomena,a brand-new method and process of sealing technique is adopted to greatly improve the situation: numbering and cleaning the studs in the preliminary process to prevent jamming during the installation of nuts,taking a new accuracy-control method to avoid leakage and rework,dividing for sealing technology and choosing different sealing solutions according to different working pressures.The experiments show that the new method significantly upgrades the reliability,availability,security and efficiency of the sealing technique.